Simultaneous beamforming and multiple input-multiple output (mimo) schemes in radar system

ABSTRACT

A radar system comprises a set of transmitters and a processor coupled to the set of transmitters. The processor is configured to modulate a first portion of a chirp in a chirp frame according to a first phase. The processor is further configured to modulate a second portion of the chirp in the chirp frame according to a second phase and configured to combine the first and second portions of the chirp to produce a phase-modified chirp. The processor is further configured to instruct the set of transmitters to transmit the phase-modified chirp by applying time division multiple access (TDMA) and by directing radio frequency energy according to a target angle and a target gain.

BACKGROUND

Radar systems are widely deployed and used in various applications forconsumer and government use. System components in radar systems varydepending on the end application. Transmitter beamforming and multipleinput-multiple output (MIMO) are two different operation modes for aradar system. Transmitter beamforming can enhance the detection rangeover a limited field-of-view by shaping the beam at the transmitter.Transmitter beamforming is achieved by applying phase shifts to theindividual transmitters resulting in a shaped beam due toconstructive/destructive interference of the transmitted beams from anantenna array of the radar system. MIMO achieves more precise angleresolution with an extensive field of view. The extensive field of viewis achieved using a plurality of transmitter modules coupled to aprocessing unit which controls signal transmissions and signalprocessing. The two operation modes typically operate independently fordifferent applications.

SUMMARY

In accordance with at least one example of the disclosure, a radarsystem comprises a set of transmitters and a processor coupled to theset of transmitters. The processor is configured to modulate a firstportion of a chirp in a chirp frame according to a first phase. Theprocessor is further configured to modulate a second portion of thechirp in the chirp frame according to a second phase and configured tocombine the first and second portions of the chirp to produce aphase-modified chirp. The processor is further configured to instructthe set of transmitters to transmit the phase-modified chirp by applyingtime division multiple access (TDMA) and by directing radio frequencyenergy according to a target angle and a target gain.

In accordance with at least one example of the disclosure, a radarmethod comprises a processor of a radar system generating a chirp framecomprising a plurality of linear frequency modulated chirps. The radarmethod comprises modulating a first portion of a chirp of the pluralityof linear frequency modulated chirps according to a first phase andmodulating a second portion of the chirp in the chirp frame according toa second phase. The radar method comprises combining the first andsecond portions of the chirp to produce a phase-modified chirp andinstructing a set of transmitters of the radar system to transmit thephase-modified chirp by applying TDMA and by directing radio frequencyenergy according to a target angle and a target gain. The radar methodcomprises demodulating a received signal to obtain the chirp based on adifference in phase values of the first phase and the second phase.

In accordance with at least one example of the disclosure, anon-transitory computer-readable medium comprises executable code,which, when executed by a processor, causes the processor to identifyphase centers of an antenna architecture of a radar system to obtain avirtual element array. The non-transitory computer-readable mediumcauses the processor to modulate a first portion of a chirp in a chirpframe according to a first phase and modulate a second portion of thechirp in the chirp frame according to a second phase. The non-transitorycomputer-readable medium causes the processor to combine the first andsecond portions of the chirp to produce a phase-modified chirp. Thenon-transitory computer-readable medium causes the processor to instructa set of transmitters of the radar system to transmit the phase-modifiedchirp by applying TDMA based on the phase centers and by directing radiofrequency energy according to a target angle and a target gain accordingto the virtual element array.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 is a block diagram of a radar system according to an example ofthis disclosure.

FIG. 2 is a block diagram of a radar system according to an example ofthis disclosure.

FIG. 3 is a block diagram of a radar system according to an example ofthis disclosure.

FIG. 4 is an illustration of a radar system according to an example ofthis disclosure.

FIGS. 5A-5C are illustrations of chirp patterns of a chirp set accordingto an example of this disclosure.

FIG. 6 is an illustration of a virtual array of antennas according to anexample of this disclosure.

FIG. 7 is a flow diagram of a method for a radar system according to anexample of this disclosure.

DETAILED DESCRIPTION

Modern vehicles include various types of sensors. A radar system is anexample of such a sensor. A radar system in a vehicle may detect safetyhazards, such as vehicles in adjacent lanes or pedestrians. For thevehicle to safely operate in a variety of driving conditions, the radarsystem in the vehicle should have long detection range and high rangeand angle resolution over a wide field-of-view.

In some technologies, hardware limitations make it difficult tosimultaneously achieve long detection range and high angle resolutionover a wide field-of-view. Consequently, one of these features can beimproved only at the expense of the other. This difficulty may beresolved by implementing additional hardware in the radar system, butthe added hardware would increase vehicular weight, costs, and technicalcomplexity.

This disclosure describes various examples of a radar system that isconfigured to use both beamforming and MIMO schemes simultaneously toachieve long detection range and high angle resolution. An antenna arrayof the radar system includes a plurality of transmitters that aregrouped into transmitter sets. Each transmitter set achieves highcoherent gain for long detection range by implementing transmitterbeamforming. In addition, a first MIMO scheme, Doppler division multipleaccess (DDMA), is applied to the transmitter sets for higher angleresolution. Further, a second MIMO scheme, TDMA, is applied to thetransmitter sets that share common transmitters to further increasevirtual array size. With the combination of transmitter beamforming andMIMO schemes (e.g., TDMA and DDMA), the radar system described hereinsimultaneously achieves long detection range and high angle resolution.The radar system described herein may be implemented in both vehicularand non-vehicular applications.

Transmit beamforming is a technique that focuses radio frequency (RF)energy from the radar system in a particular direction. The side to sidedirection is commonly referred to as the azimuth and the up and downdirection as the elevation. Beamforming can be used to focus the radarover both azimuth and elevations. This can be accomplished byprogramming each transmit channel with a specific phase value, such thatthe radiation power is sent towards a desired direction when enablingall the TX at the same time. The phase value programmed to each TXchannel is calculated based on the antenna positions and the desiredangle to steer the beam. In addition, TX beamforming requires thesilicon to provide a way to precisely program the phase value for eachTX channel.

The DDMA waveform ensures orthogonality of the transmit signals andavoids some of the problems in the application of Frequency DivisionMultiple Access (FDMA) and Code Division Multiple Access (CDMA) for theradar system. The DDMA waveform achieves signal separation by shiftingthe transmit signals of different transmitters to different Dopplerfrequencies indicated by a change in phase of the signal.

The TDMA waveform includes a precision timing requirement beyondstarting and stopping the channel. Unique time slots are defined withina repeating frame such that a single frequency band can service multipletransmitters. Each transmitter adheres to the respective time slot toavoid interference between the transmitters.

While aspects herein are described primarily in the context of a radarsystem in use with a vehicle, these aspects may also be applicable toany system or circuit on any type of vehicle. For example, the examplemethods and systems described in this disclosure can be similarlyapplied to a circuit mounted to an aircraft, a motorcycle, a drone, orthe like. As another example, the example methods and systems describedin this disclosure can be similarly applied to a utility vehicle forindustrial applications. These and other aspects are described ingreater detail below.

FIG. 1 illustrates an example radar system 100. As shown, the radarsystem 100 includes a transceiver terminal 102 and a plurality ofantennas 104. In some examples, the transceiver terminal 102 and theantennas 104 are installed within a vehicle. In an example, thetransceiver terminal 102 generates a signal to send to the antennas 104.The signal comprises a plurality of chirps to determine a distance ofobjects within the beam-width of the antennas 104. The radar system 100compares a time when the signal is sent to the time the signal isreceived to determine the distance of objects within the beam-width ofthe antennas 104. In an example, the vehicle is a self-driving vehicle,an aircraft, a motorcycle, a drone, or the like.

In an example, the transceiver terminal 102 is a software defined radio(SDR), a field-programmable gate array (FPGA), an application-specificintegrated circuit (ASIC), a digital signal processor (DSP), or thelike. In an example, the radar system 100 can transmit a radio frequency(RF) signal between 76 gigahertz (GHz) and 81 GHz, but is not limited tothis frequency range depending on the application.

In an example, the antennas 104 are in an antenna array design based onapplying a genetic algorithm (GA) to search for the optimal arrayelement position, suppress the MIMO pattern grating lobe, and improvethe direction-of-arrival (DOA) estimation performance. In an example,the antennas 104 include a one-dimensional array of elements, where theelements are uniformly spaced from one another and emit electromagneticenergy in an omnidirectional pattern. In an example, the antennas 104are categorized as monopoles, dipoles, slot antennas, or the like.

In an example, the radar system 100 can achieve both short range andmid-range detection and maintain a high-precision angle resolution.Short range is considered to be 0 meters (m) to 50 m, mid-range isconsidered to be 50 m to 120 m, and long range is considered to be 120 mto 150 m or greater. A high-precision angle resolution is considered tobe a beam-width less than 10 degrees (°).

FIG. 2 illustrates an example radar system 100. As shown, the radarsystem 100 includes the transceiver terminal 102 and the antennas 104.The transceiver terminal 102 includes a plurality of transmitters 202, aprocessor 204, and a memory 206. In an example, a portion of the memory206 may be non-transitory memory and a portion of the memory 206 may betransitory memory. The transmitters 202 are coupled to the processor204. The processor 204 is coupled to the memory 206. In an example, eachof the transmitters 202 are coupled to at least one of the antennas 104.

In an example, the processor 204 generates and transmits a signal toeach of the transmitters 202. The signal indicates to the transmitters202 a frequency at which the transmitters will operate, a bandwidth foroperation, a pulse repetition frequency (PRF), a PRI, or the like. In anexample, the signal enters each of the transmitters 202 and traverses asignal chain (not shown) in each of the transmitters 202 before beingtransmitted to the antennas 104. After the signal enters thetransmitters 202, the signal is filtered by a digital filter where anyspurious bits outside of a predefined frame size are removed. After thedigital filter, the signal is provided to a digital-to-analog converter(DAC). A clock signal from the transmitters 202 are used as the clockwithin the DAC. After the DAC, the signal is further filtered by a firstlow pass filter. After the low pass filter, the signal is transmitted toan intermediate frequency (IF) amplifier. After the IF amplifier thesignal is further filtered by a second low pass filter to mitigate anyspurious signals which interfered with the signal in the IF amplifier.After the second low pass filter, the signal is provided to a mixer,where the signal is mixed with a signal from a phase locked loop (PLL)or voltage controlled oscillator (VCO) depending on the application.After the mixer, the signal passes through a third low pass filter tofilter any spurious signals which interfered with the signal in themixer. After the third low pass filter, the signal is sent to a poweramplifier which amplifies the signal. After the power amplifier, atleast one phase shifter applies phase shifts to the signal resulting ina shaped beam due to constructive/destructive interference of thetransmitted beams. The signal is transmitted to the antennas 104, wherethe signal couples with antenna elements of the antenna 104 fortransmission of electromagnetic energy through free-space.

FIG. 3 illustrates an example radar system 300. As shown, the radarsystem 300 includes a transceiver terminal 102 and a plurality ofantennas 104. The transceiver terminal 102 includes the processor 204,the memory 206, a first transmitter 302, a second transmitter 304, athird transmitter 306, a fourth transmitter 308, a first subset oftransmitters 310, a second subset of transmitters 312, a third subset oftransmitters 314, and a fourth subset of transmitters 316. The firsttransmitter 302, the second transmitter 304, the third transmitter 306,and the fourth transmitter 308 are each coupled to the processor 204 andthe antennas 104. The first transmitter 302 and the second transmitter304 are included in the first subset of transmitters 310. The secondtransmitter 304 and the third transmitter 306 are included in the secondsubset of transmitters 312. The third transmitter 306 and the fourthtransmitter 308 are included in the third subset of transmitters 314.The first transmitter 302 and the fourth transmitter 308 are included inthe fourth subset of transmitters 316. In an example, TDMA can beapplied to subsets of transmitters that share a transmitter. Forexample, the first subset of transmitters 310 and the second subset oftransmitters 312 share the second transmitter 304 using TDMA toalternate between transmitting a signal from the first subset oftransmitters 310 at a first time and transmitting a signal from thesecond subset of transmitters 312 at a second time.

In another example, DDMA can be applied simultaneously to, orindependently from, TDMA by the processor 204. Simultaneously in thiscase means operating at the same time. For example, DDMA can be appliedto the radar system 300 as follows. The processor 204 mixes signals fromthe first transmitter 302 and the second transmitter 304 and applies afirst phase change to obtain a first phase mixed signal and mixessignals from the third transmitter 306 and the fourth transmitter 308and applies a second phase change to obtain a second phase mixed signal.The processor 204 then mixes the first phase mixed signal and the secondphase mixed signal to obtain a DDMA signal. The first phase change andthe second phase change are based on Doppler shifts, which allow thefirst phase change and the second phase change to be orthogonal.

In yet another example, each of the transmitter subsets can perform TXbeamforming in addition to the TDMA/DDMA output. The beamforming isaccomplished by programming each transmit channel with a specific phasevalue, such that beam can be steered to a desired angle based onconstructive/destructive interference of the electromagnetic energy fromthe antennas 104. The phase value programmed to each TX channel iscalculated based on the antenna positions and the desired angle to steerthe beam in the processor 204. In addition, TX beamforming requires thesilicon to provide a way to precisely program the phase value for eachTX channel.

In another example, FDMA can be applied simultaneously to, orindependently from, TDMA and DDMA by the processor 204. For example, thefirst subset of transmitters 310 and the second subset of transmitters312 share the second transmitter 304 using FDMA to transmit a signalfrom the first subset of transmitters 310 at a first frequency andtransmit a signal from the second subset of transmitters 312 at a secondfrequency. The first frequency and the second frequency are orthogonalsuch that no interference occurs between the first subset oftransmitters 310 and the second subset of transmitters 312. In anotherexample, the radar system 300 can use FDMA, TDMA, and/or DDMAindividually or simultaneously. The first subset of transmitters 310,the second subset of transmitters 312, the third subset of transmitters314, and the fourth subset of transmitters 316 are not limited to theconfiguration listed above and can comprise any configuration of thefirst transmitter 302, the second transmitter 304, the third transmitter306, and the fourth transmitter 308 0.

In an example, the memory 206 comprises instructions to implement a userinterface. The user interface receives instructions from a user whichcan control the radar system 300 to operate in various operation modes.In an example, the operation modes correspond with beamforming and MIMO,where an operation mode corresponding with MIMO comprises a plurality ofoptions such as TDMA, DDMA, and FDMA. The user can select whichoperation mode best suits the application of the radar system 300. Forexample, the user can select only to apply TDMA when the radar system isconfigured to medium range resolution.

FIG. 4 illustrates an example radar system 400. As shown, the radarsystem 400 includes the processor 204, the first transmitter 302, thesecond transmitter 304, the third transmitter 306, the fourthtransmitter 308, the first subset of transmitters 310, the second subsetof transmitters 312, the third subset of transmitters 314, the fourthsubset of transmitters 316, a first antenna 402, a second antenna 404, athird antenna 406, and a fourth antenna 408. The processor 204 iscoupled to each of the first transmitter 302, the second transmitter304, the third transmitter 306, and the fourth transmitter 308. Thefirst transmitter 302 is coupled to the first antenna 402, the secondtransmitter 304 is coupled to the second antenna 404, the thirdtransmitter 306 is coupled to the third antenna 406, and the fourthtransmitter 308 is coupled to the fourth antenna 408.

In an example, according to a first time by applying TDMA, the firsttransmitter 302 and the second transmitter 304 of the first subset oftransmitters 310 and the third transmitter 306 and the fourthtransmitter 308 of the third subset of transmitters 314 are active. Theprocessor 204, by applying DDMA, shifts phase components of signals fromthe first transmitter 302 and the second transmitter 304 by a firstphase amount corresponding to a Doppler frequency of the application ofthe radar system 400. Further, the processor 204, by applying DDMA,shifts phase components of signals from the third transmitter 306 andthe fourth transmitter 308 by a second phase amount corresponding to theDoppler frequency. The first transmitter 302, the second transmitter304, the third transmitter 306, and the fourth transmitter 308 outputthe signals to the first antenna 402, the second antenna 404, the thirdantenna 406, and the fourth antenna 408. The signals radiating from eachof the first antenna 402, the second antenna 404, the third antenna 406,and the fourth antenna 408 combine to generate a first chirp. In anexample, the processor 204, by applying beamforming, shifts the phasecomponents of the signals from the first transmitter 302 and the secondtransmitter 304 by a first phase offset and shifts phase components ofsignals from the third transmitter 306 and the fourth transmitter 308 bya second phase offset. The first phase offset and the second phaseoffset result in the output of the signals from the first antenna 402,the second antenna 404, the third antenna 406, and the fourth antenna408 to constructively/destructively interfere and direct the beam of theradar system 400. In an example, the first phase offset and the secondphase offset correspond to angles that cause interference of the beam ofthe radar system 400 to be directed up to +/−90° from the azimuth of theradar system 400 and/or 180° in elevation.

In another example, according to a second time by applying TDMA, thefirst transmitter 302 and the fourth transmitter 308 of the fourthsubset of transmitters 316 and the second transmitter 304 and the thirdtransmitter 306 of the second subset of transmitters 312 are active. Theprocessor 204, by applying DDMA, shifts phase components of signals fromthe first transmitter 302 and the fourth transmitter 308 by the firstphase. Further, the processor 204, by applying DDMA, shifts phasecomponents of signals from the second transmitter 304 and the thirdtransmitter 306 by the second phase. The first transmitter 302 outputs afirst signal to the first antenna 402, the second transmitter 304outputs a second signal to the second antenna 404, the third transmitter306 outputs a third signal to the third antenna 406, and the fourthtransmitter 308 outputs a fourth signal to the fourth antenna 408. Thesignals radiating from each of the first antenna 402, the second antenna404, the third antenna 406, and the fourth antenna 408 combine togenerate a second chirp. In an example, the processor 204, by applyingbeamforming, shifts the phase components of the signals from the firsttransmitter 302 and the fourth transmitter 308 by a first phase offsetand shifts phase components of signals from the second transmitter 304and the third transmitter 306 by a second phase offset. The signalsshifted by the first phase offset and the second phase offset result inthe output of the signals from the first antenna 402, the second antenna404, the third antenna 406, and the fourth antenna 408 toconstructively/destructively interfere to direct the beam of the radarsystem 400. In an example, the first phase offset and the second phaseoffset correspond to angles that cause interference of the beam of theradar system 400 to be directed up to +/−90° from the azimuth and 180°in elevation.

FIG. 5A illustrates an exemplary chirp set 500 from the radar system 400comprising different patterns according to TDMA and DDMA. Chirp 1 502,chirp 3 506, and chirp N 510 of the chirp set 500 correspond to a firstpattern based on a first time set. Chirp 2 504, chirp 4 508, and chirpN+1 512 correspond to a second pattern based on a second time set. Chirp1 502 is based on the first pattern at a first time of the first timeset and comprises a mixed signal from outputs of a first transmittersubset and a second transmitter subset. The first transmitter subsetoutputs signals from a first transmitter and second transmitter that areshifted by a first phase. The second transmitter subset outputs signalsfrom a third transmitter and a fourth transmitter shifted by a secondphase. Chirp 2 504 is based on the second pattern at a first time of thesecond time set and comprises a mixed signal from outputs of a thirdtransmitter subset and a fourth transmitter subset. The thirdtransmitter subset outputs signals from the first transmitter and thefourth transmitter that are shifted by the first phase. The fourthtransmitter subset outputs signals from the second transmitter and thethird transmitter shifted by the second phase. The first pattern and thesecond pattern alternate based on a time duration of each the first timeset and the second time set for the remaining chirps of the chirp set500. Each time the pattern alternates for the chirp set 500, a new timeframe of either the first time set or the second time set occurs basedon the TDMA scheme. Alternating between the first pattern and the secondpattern allows the radar system 400 to achieve simultaneous applicationof TDMA and DDMA. In an example, the radar system 400 additionally isconfigured to receive a signal corresponding with the chirp set 500 anddemodulate the signal based on the first pattern and the second pattern.The first pattern and the second pattern are the same as describedabove. The radar system 400 is able to demodulate the chirp set 500according to the first pattern and the second pattern such that theradar system 400 obtains information of the chirps and determine thecorresponding transmitters for further signal processing by the radarsystem 400 to form a virtual MIMO array which provides angle of arrivalinformation. FIG. 5B illustrates the chirp 1 502, the chirp 3 506, andthe chirp N 510 of the chirp set 500 that correspond to the firstpattern based on the first time set. FIG. 5C illustrates chirp 2 504,chirp 4 508, and chirp N+1 512 of the chirp set 500 that correspond tothe second pattern based on the second time set. In an example, thechirp set 500 can follow various patterns not included in thisdisclosure. For example, the chirp set 500 can follow three patterns ormore based on the application of the radar system 400.

In an example, the time duration of each chirp of the chirp set 500 canbe between 20 microseconds (μs) and 30 μs, but is not limited to thisrange depending on the application. In an example, the number of chirpsin the chirp set 500 can be between 64 and 512, but is not limited tothis range depending on the application.

FIG. 6 illustrates an example MIMO configuration 600. As shown, the MIMOconfiguration 600 includes the first antenna 402, the second antenna404, the third antenna 406, the fourth antenna 408, a first phase center602, a second phase center 604, a third phase center 606, a virtualarray 608, a first set of virtual elements 610, a second set of virtualelements 612, and a third set of virtual elements 614.

In an example, the arrangement of the first antenna 402, the secondantenna 404, the third antenna 406, and the fourth antenna 408 createsphase centers at the first phase center 602, the second phase center604, and the third phase center 606. A phase center is a location of apoint associated with the antenna such that, if it is taken as thecenter of a sphere whose radius extends into the far-field, the phase ofa given field component over the surface of the radiation sphere may beconstant, at least over that portion of the surface where the radiationis significant. In an example, the distance between antennas is twotimes the wavelength (2X) for the application which makes the outputfrom each of the antennas orthogonal to each of the adjacent antennas.

In an example, from a radar system using TDMA and DDMA, the radar systemcan transmit a signal with reference to each of the first phase center602, the second phase center 604, and the third phase center 606 whichresults in the first set of virtual elements 610, the second set ofvirtual elements 612, and the third set of virtual elements 614. Thevirtual elements correspond to each phase center acting as anindependent emission source to the other phase centers and has access toeach antenna independently. The virtual elements can improve the degreeof freedom and the angle of estimation resolution performance of theradar system. For example, in a typical MIMO system with four antennas,the orthogonality between the phase centers can be used to achieve aneffective transmission of four phase centers across the four antennasresulting in 16 virtual elements.

In examples of this disclosure, the radar system 400 simultaneouslyapplies TDMA and DDMA. The simultaneous use of TDMA and DDMA results inan increase of range and beam-width achievable by the radar system 400.However, the simultaneous use of TDMA and DDMA decreases the totalnumber of available virtual elements of the array down from 16 virtualelements to 12 virtual elements. The decrease in virtual elements isbased on the radar system 400 having transmitter subsets, where thephase centers of two transmitter subsets overlap. The overlap of thephase centers makes only one phase center useful for the MIMOconfiguration.

FIG. 7 is a flow chart of an example method 700 for a radar system. Themethod 700 includes generating a chirp frame comprising a plurality oflinear frequency modulated chirps (702).

The method 700 includes modulating a first portion of a chirp of theplurality of linear frequency modulated chirps according to a firstphase (704).

The method 700 includes modulating a second portion of the chirp in thechirp frame according to a second phase (706).

The method 700 includes combining the first and second portions of thechirp to produce a phase-modified chirp (708).

The method 700 includes instructing a set of transmitters of the radarsystem to transmit the phase-modified chirp by applying time divisionmultiple access (TDMA) and by directing RF energy according to a targetangle and a target gain (710).

The method 700 includes demodulating a received signal to obtain thechirp based on a difference in phase values of the first phase and thesecond phase (712).

The term “couple” is used throughout the specification. The term maycover connections, communications, or signal paths that enable afunctional relationship consistent with this description. For example,if device A generates a signal to control device B to perform an action,in a first example device A is coupled to device B, or in a secondexample device A is coupled to device B through intervening component Cif intervening component C does not substantially alter the functionalrelationship between device A and device B such that device B iscontrolled by device A via the control signal generated by device A.

A device that is “configured to” perform a task or function may beconfigured (e.g., programmed and/or hardwired) at a time ofmanufacturing by a manufacturer to perform the function and/or may beconfigurable (or re-configurable) by a user after manufacturing toperform the function and/or other additional or alternative functions.The configuring may be through firmware and/or software programming ofthe device, through a construction and/or layout of hardware componentsand interconnections of the device, or a combination thereof.

A circuit or device that is described herein as including certaincomponents may instead be adapted to be coupled to those components toform the described circuitry or device. For example, a structuredescribed as including one or more semiconductor elements (such astransistors), one or more passive elements (such as resistors,capacitors, and/or inductors), and/or one or more sources (such asvoltage and/or current sources) may instead include only thesemiconductor elements within a single physical device (e.g., asemiconductor die and/or integrated circuit (IC) package) and may beadapted to be coupled to at least some of the passive elements and/orthe sources to form the described structure either at a time ofmanufacture or after a time of manufacture, for example, by an end-userand/or a third-party.

While certain components may be described herein as being of aparticular process technology, these components may be exchanged forcomponents of other process technologies. Circuits described herein arereconfigurable to include the replaced components to providefunctionality at least partially similar to functionality availableprior to the component replacement. Components shown as resistors,unless otherwise stated, are generally representative of any one or moreelements coupled in series and/or parallel to provide an amount ofimpedance represented by the shown resistor. For example, a resistor orcapacitor shown and described herein as a single component may insteadbe multiple resistors or capacitors, respectively, coupled in parallelbetween the same nodes. For example, a resistor or capacitor shown anddescribed herein as a single component may instead be multiple resistorsor capacitors, respectively, coupled in series between the same twonodes as the single resistor or capacitor.

Uses of the phrase “ground voltage potential” in the foregoingdescription include a chassis ground, an Earth ground, a floatingground, a virtual ground, a digital ground, a common ground, and/or anyother form of ground connection applicable to, or suitable for, theteachings of this description. Unless otherwise stated, “about,”“approximately,” or “substantially” preceding a value means+/−10 percentof the stated value. Modifications are possible in the describedexamples, and other examples are possible within the scope of theclaims.

What is claimed is:
 1. A radar system, comprising: a set oftransmitters; and a processor coupled to the set of transmitters, theprocessor configured to: modulate a first portion of a chirp in a chirpframe according to a first phase; modulate a second portion of the chirpin the chirp frame according to a second phase; combine the first andsecond portions of the chirp to produce a phase-modified chirp; andinstruct the set of transmitters to transmit the phase-modified chirp byapplying time division multiple access (TDMA) and by directing radiofrequency energy according to a target angle and a target gain.
 2. Theradar system of claim 1, wherein: the set of transmitters includes afirst subset of transmitters and a second subset of transmitters, thefirst and second subsets having a transmitter in common, and theprocessor is configured to instruct the first and second subsets totransmit, using TDMA, the phase-modified chirp and additional chirps ofthe chirp frame.
 3. The radar system of claim 2, wherein the processoris configured to: receive a signal including the phase-modified chirp;and perform a Doppler fast Fourier transform (FFT) on the receivedsignal.
 4. The radar system of claim 2, wherein the processor isconfigured to combine the first and second portions of the chirp toproduce the phase-modified chirp based on applying Doppler divisionmultiple access (DDMA).
 5. The radar system of claim 4, wherein the setof transmitters is configured to transmit, using TDMA, DDMA, andbeamforming simultaneously, the phase-modified chirp.
 6. The radarsystem of claim 2, wherein the processor is configured to instruct thefirst and second subsets to transmit the phase-modified chirp and theadditional chirps based on a first pattern.
 7. The radar system of claim6, wherein the processor is configured to instruct the first and secondsubsets to transmit the phase-modified chirp and the additional chirpsbased on a second pattern, wherein the first pattern and the secondpattern alternate based on a time duration.
 8. A radar method,comprising: a processor of a radar system generating a chirp framecomprising a plurality of linear frequency modulated chirps; theprocessor modulating a first portion of a chirp of the plurality oflinear frequency modulated chirps according to a first phase; theprocessor modulating a second portion of the chirp in the chirp frameaccording to a second phase; the processor combining the first andsecond portions of the chirp to produce a phase-modified chirp; and theprocessor instructing a set of transmitters of the radar system totransmit the phase-modified chirp by applying time division multipleaccess (TDMA) and by directing radio frequency energy according to atarget angle and a target gain; and the processor demodulating areceived signal to obtain the chirp based on a difference in phasevalues of the first phase and the second phase.
 9. The radar method ofclaim 8, wherein the radar system is embedded in a vehicle and furthercomprising detecting an obstacle on a roadway on which the vehicle isdriving by the processor.
 10. The radar method of claim 9, wherein: theset of transmitters includes a first subset of transmitters and a secondsubset of transmitters, the first and second subsets having atransmitter in common, and the radar method further comprises:instructing the first and second subsets to transmit the phase-modifiedchirp and additional chirps of the chirp frame using TDMA; andperforming a Doppler fast Fourier transform (FFT) on the receivedsignal.
 11. The radar method of claim 10, further comprising: theprocessor instructing the first and second subsets to transmit thephase-modified chirp and the additional chirps based on a first pattern.12. The radar method of claim 11, further comprising: the processorinstructing the first and second subsets to transmit the phase-modifiedchirp and the additional chirps based on a second pattern, wherein thefirst pattern and the second pattern alternate based on a time duration.13. The radar method of claim 9, further comprising: the processorcombining the first and second portions of the chirp to produce thephase-modified chirp based on applying Doppler division multiple access(DDMA).
 14. The radar method of claim 13, further comprising: theprocessor instructing the set of transmitters to transmit thephase-modified chirp using TDMA, DDMA, and beamforming simultaneously.15. A non-transitory computer-readable medium storing executable code,which, when executed by a processor, causes the processor to: identifyphase centers of an antenna architecture of a radar system to obtain avirtual element array; modulate a first portion of a chirp in a chirpframe according to a first phase; modulate a second portion of the chirpin the chirp frame according to a second phase; combine the first andsecond portions of the chirp to produce a phase-modified chirp; andinstruct a set of transmitters of the radar system to transmit thephase-modified chirp by applying time division multiple access (TDMA)based on the phase centers and by directing radio frequency energyaccording to a target angle and a target gain according to the virtualelement array.
 16. The computer-readable medium of claim 15, wherein:the set of transmitters includes a first subset of transmitters and asecond subset of transmitters, the first and second subsets having atransmitter in common, and the executable code further causes the radarsystem to instruct the first and second subsets to transmit, using TDMA,the phase-modified chirp and additional chirps of the chirp frame. 17.The computer-readable medium of claim 16, wherein the executable codefurther causes the radar system to: receive a signal including thephase-modified chirp; and perform a Doppler fast Fourier transform (FFT)on the received signal.
 18. The computer-readable medium of claim 16,wherein the executable code further causes the radar system to combinethe first and second portions of the chirp to produce the phase-modifiedchirp based on applying Doppler division multiple access (DDMA).
 19. Thecomputer-readable medium of claim 18, wherein the executable codefurther causes the radar system to instruct the set of transmitters totransmit, using TDMA, DDMA, and beamforming simultaneously, thephase-modified chirp.
 20. The computer-readable medium of claim 16,wherein the executable code further causes the radar system to: instructthe first and second subsets to transmit the phase-modified chirp andthe additional chirps based on a first pattern; and instruct the firstand second subsets to transmit the phase-modified chirp and theadditional chirps based on a second pattern, wherein the first patternand the second pattern alternate based on a time duration.